Piezoelectric controlled oscillator



Feb. 13, 1940.

A. SAMUEL 7 2,189,770

PIEZOELECTRIC CONTROLLED OSCILLATOR Filed July 19, 1958 l l il INVENTOR A L. SAMUEL ATTORNEY Patented Feb. 13, 1940 UNITED STATES PATENT oF-FicE 2,189,770 I rmzonmcrmc CONTROLLED OSCILLATOR Arthur L. Samuel, Summit, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York ,Application July 19,1938, Serial No. 219,959

14 Claims.

ing electrode circuits as to minimize couplings therebetween and to reduce their effect upon frequency control and stability.

The operation of electron discharge amplifiers at high frequencies has been attended with the difficulty that feedback from the anode to a control element through the interelectrode ca- Dacitance between the electrode and the control element tends to cause the apparatus to oscillate. A circuit designed to prevent such oscillation is that of Patent 1,325,879 issued De- 26 cember 23, 1919 to H. W. Nichols. With theadvent of oscillations of a few centimeters in wave-length it has been found that additional couplings between the anode circuit and that of the control element are introduced by other mutual reactances notably those of the discharge device. An ultra high frequency amplifier designed to minimize these additional couplings of the electrode leads and to introduce other improvements in the design of the electron discharge device and its associated circuits is disclosed in the copending application of A. L. Samuel, Serial No. 78,594 filed May 8, 1936. In accordance with the present invention it is proposed to utilize a neutralized amplifier of any of the types disclosed in that application by introducing into the neutralizing circuit a piezoelectric element so connected that the circuit will behave as a neutralized amplifier except at or near those frequencies corresponding to resonant modes of the piezoelectric device. At such frequencies conditions for stability will not be satisfiedand oscillations may occur. In effect, the piezoelectric device prevents the circuit from oscillating except within certain definite regions. If, therefore, these regions fall within the effective amplification band of the amplifier, the device may serve as a source of ultra high frequency oscillations of a very stable and welldefined frequency. As an alternative, the piezoelectric device may constitute an element of the cathode-control element circuit or the cathodeanode circuit. I 7

Additional aspects and features of the inven-' tion will become apparent upon consideration v of the following detailed description in c'onnec- 5 tion with the accompanying drawing, of which:

Fig. 1 shows a schematic circuit diagram of one embodiment of the invention;

Figs. 2, 3 and 4 illustrate modifications of circuit of Fig. 1;

Figs; '5 and 6 illustrate oscillating systems in which the piezoelectric element is included in the cathode-control element circuit; and

Figs. 7 and 8'show oscillator circuits having the the piezoelectric element in the cathode-anode circuit.

Referring to Fig. 1 the oscillator circuit comprises an electron discharge device l'which, as illustrated, includes a cathode 2, an anode 3 and a control element 4. The electrodes'are- 2 0 each provided with two separate leads to elim-' mate the mutual reactance or coupling involved when a single lead is used to connect the same electrode to two or more circuits. Preferably, the electron discharge device conforms in struc- 25 ture to one of the disclosures of Figs. 1,2, 3, 9- or 10 of my c'opending application, Serial No. '78,-594 filed May 8, 1936. Accordingly, the different leads to an individual electrode may be brought out from the electron discharge device 30 at widely separated points andin some instances.

at opposite sides or ends of the tube as disclosed in the copending application. It is to be understood that the disclosures of that application are effectively incorporated in this speci- 35 fication although the electron discharge device is in each instance illustrated herein diagrammatically for the sake of simplicity. It is also to be understood that although in each instance the electron discharge device is illustrated herein 0 as a triode, the principles of the invention are equally applicable to multi-electrode discharge devices'of any kind which are capable of transmitting oscillations of the order of a few centimeters in wave-length. 'The oscillator circuit 45 of Fig. 1 involves three external circuits 5, 6' and I, each connected between a pair of electrodes. Tuned circuit 5 comprising an inductance and capacity connected between the control electrode 4 and the cathode 2 may herein- 50 after be referred to as the input circuit because of its analogy to the input circuit of the usual vacuum tube amplifier. Tuned circuit 6 including -an:inductance and a capacity element and generally similar to circuit 5, connected between 55 the anode 3 and cathode 2 may likewise be referred to as the output circuit. A loop 1 comprising an inductance and a piezoelectric element 12 in shunt thereto is connected to the control element 4 and through a large capacity blocking condenser 8 to the anode 3. The oscillator circuit also includes the polarizing sources 9, l0 and II of any well-known types.

The piezoelectric element i2 is so designed and constructed as to have a natural resonance frequency or a harmonic resonance frequency at the frequency of the oscillations which it is dc sired to produce. Under non-oscillating conditions the device 12 may be regarded as a static,

capacity element. In shunt to that capacity element is a capacity path including the large blocking condenser 8 in series with the interelectrode capacitance between theanode 3 and the control element 4. If the inductance element of the circuit I be so designed that to' gether withthe static capacitance of the element l2 and the shunt path by way of element 8 the circuit be resonant to a particular frequency it will, during a non-oscillating condition of the device I2, function to neutralize the effect of interelectrode capacitance between the elements 3 and 4 at the frequency to which the circuit 1 is tuned in accordance with the principle disclosed in U. S. Patent 1,325,879, issued December 23, 1919, to H. W. Nichols. Under these circumstances if the circuits 5 and 6 be tuned to substantially the same frequency as the circuit 7 there may be no feedback from the circuit 6 to the circuit 5 through the internal interelectrode capacitance of the device. If, in addition to this precaution, the leads to the circuits 5, B and I be widely separated to reduce any mutual or coupling effects the device will constitute a neutralized amplifier of the general type disclosed in the Nichols patent and more specifically disclosed in the copending application, Serial No. 78,594 to which reference has already been made. The separation of these leads is indicated diagrammatically in the drawing and the structures for effectively securing such separation are fully disclosed in the copending application, Serial No. 78,594.

The effect of the piezoelectric element I2 is to upset the neutralizing condition at or near those frequencies corresponding to the resonance modes of the piezoelectric element, Accordingly, while oscillations within the effective transmission band of the circuits 5 and 6 will normally be prevented by the neutralizing circuit, the piezoelectric element permits oscillations within that band provided that they are sufficiently close to its resonance frequency. It is possible, therefore, to cause the device to oscillate at a selected resonance frequency or a selected harmonic frequency of the piezoelectric element if that frequency falls in the effective transmission band of the circuits 5 and 6.

Fig. 2 discloses an oscillator similar'to that of Fig. 1 and differing only in that the piezoelectric element I3 is connected between the tuned loop 7 and the anode instead of directly in the tuned loop. It will be understood, of course, that the tuned loop circuit 7 together with the shunt path including the static capacity of the device I3 in series with the interelectrode capacitance between anode 3 and the control element 4 should be made resonant to substantially the resonance frequency of circuits 5 and 6 so as to neutralize the feedback between the circuits 6 and 5 within the effective frequency transmission band of the circuits 5 and 6 except at or near the selected resonance frequency of the piezoelectric device l3.

The oscillator circuit of Fig. 3 differs from that of Fig. 2 only in the omission of the capacity element M. In this instance the resonant or tuned loop includes in series the inductance, piezoelectricelement l5 and the interelectrode capacitance between electrodes 3 and 4 of the electron discharge device.

Fig. 4 illustrates an electron discharge oscillator in accordance with the invention in which the tuned loops 5, 6 and l of the preceding figures are each replaced by a Lecher circuit such as I8, .I1 and I8. As is well known, the Lecher circuit comprises closely adjacent parallel conductors which function as a distributed capacity and inductance. At the terminals adjacent the electron discharge device the Lecher circuit is connected to the interelectrode impedance of the two electrodes with which it is associated. At its outer'terminal the Lecher circuit is effectively terminated by a short-circuiting capacity element, such as element IQ, of relatively large capacity provided with sliding terminal connections to enable tuning in well-known manner. Such a piezoelectric circuit will ordinarily be constructed of an odd number of quarter wavelengths at the desired oscillation frequency. The neutralizing circuit I8 connected between the anode 3 and control element 4 may be terminated by a piezoelectric device which, as in the case of the preceding circuits, permits oscillations to take place at a selected resonance frequency of the device within the effective transmission band of the circuits [6 and I1 but which does not interfere with the neutralizing function of the circuit l8 at other frequencies within that band, As in the case of the capacity element l8 the'piezoelectric element 20 is mounted with a slidable terminal connection to properly tune the circuit [8. In addition to the other expedients for preventing oscillation due to fortuitous coupling, the circuits [6 and Il may be extended in opposite directions from the electron discharge device and the circuit [8 at right angles thereto as indicated schematically in the drawing.

' Fig. 5 shows a modified oscillator circuit with the piezoelectric element 2| included in the input circuit. A variable tuning condenser 22 enables the input circuit to be tuned. The grid and anode are indicated with leads at their opposite ends in accordance with the disclosure of application Serial No. 78,594 to eliminate coupling of their individual external circuits which might otherwise be introduced. Moreover, although the circuits of Figs. 1 to 4, inclusive, are shown diagrammatically with the control element'leads and the anode leads at a single end of the respective electrode, it is to be understood that opposite end lead connections like those of Fig. 5 may be used in each of the circuits of Figs. 1 to 4 for the control element and the anode and, moreover, where linear cathodes are employed for the cathode as Well.

Fig. 6 presents a circuit differing from that of Fig. 5 only in that the inductance coil piezoelectric element 24, and auxiliary condenser 23 of the tuned input circuit are connected in series to form the closed loop instead of in parallel as in Fi 5.

Fig. 7 illustrates another oscillator of the neutralized amplifier type in which the piezoelectric element 25 is connected in the output circuit in shunt to the inductance coil in the same manner as the element 2| in the input circuit of Fig. 5. Fig. 8 shows a further modification in which the piezoelectric element 26 is connected in series with an auxiliary condenser 21 and an inductance coil to constitute a tuned loop circuit similar to the input circuit of Fig. 6-.

In each of the figures; the polarizing sources for the control element and the anode are shown as in Fig. l as is also the cathode heating source. It will be apparent that in the circuit of Fig. 4 the Lecher conductors may serve as the unidirectional path for each of the three external circuits since the terminating condensers effectively short-circuit the Lecher paths and preclude any effect of the short-circuited outer portions of the Lecher conductors upon the tuned portions. It will also be understood that as in Fig. 1, very large capacity-blockingcondensers 8 may be utilized in the circuits of Figs. 5 to 8, inclusive, to protect the control element from the high positive potential of the anode polarizing source.

It will be unnecessary to explain the operation of the circuits of Figs. .5 to 8, inclusive. in detail since it will of course be understood that in each instance the tuned circuit between the control element and the anode includin capacitance I4 together with the path including blocking condenser 8 and the inherent interelectrode capacitance between the anode and the control element is made antiresonant at the resonance freouency of the in ut and output circuits to constitute a neutralized amplifier. The piezoelectric elements 2l, 23, and 26 may each have a mode of resonance of a fundamental or of a harmonic ty e at a single freouency within the efi'ective transmission band of the input and output circu ts of the amplifier. Accordingly, at that sin le freouency the piezoelectric element may upset the neutralized condition and permit oscillations to occur.

As ex lained in the specification of application Serial No. 78.594, the electron dischar e device may be so designed as to cause nodes to occur at the points where the lead-in wires pass through the dielectric envelope of the discharge device.

. What is claimed is: I

1. In combination. an electron discharge device having -a plurality of electrodes including a cathode, an anode and a control element. and three individual circuits connected. respectively between the cathode and the anode, the cathode and the control element and the anode and the control element each of the three circuits comprisin a tuned loop. the circuit connecting the anode and the control element and including the anode-control element interelectrode capac tance being anti-resonant at the resonance frecluencv of the other two individual circuits to constitute a neutralized amplifier and a piezoelectric element connected in one of the three individual circuits and having a mode of oscillation at a single frequency within the effective transmission band of the two circuits which connect the anode to the cathode and the control element to the cathode.

2. The combination of claim 1, characterized in this, that the piezoelectric element is connected in the circuit between the cathode and the control element. I

3. The combination of claim 1, characterized in this, that the piezoelectric element is connected in the circuit between the cathode and the anode.

4. In combination, an electron discharge device having a plurality of electrodes including a cathode, an anode and a control element, and three individual circuits connected respectively be tween the cathode and the anode, the cathode and the control element and the anode andthe control element, each of the three circuits comprising a tuned loop, the circuit connecting the anode and the control element including a piezoelectric element having a mode of oscillation within the frequency region closely adjacent the resonant frequencies of the loops of the other two circuits.

5. The combination of claim 4, characterized in this, that the tuned loop of the circuit between the control element and the anode includes the inherent interelectrode capacitance between the control element and the anode.

6. The combination of claim 4, characterized in this, that the leads from the electrodes to each individual circuit are separate from the leads to the other individual circuits so as not to introduce a mutual reactance.

7. The combination of claim 4, characterized in this, that the piezoelectric element has a harmonic frequency mode of oscillation within the effective transmission band of the input and output circuits which respectively connect the control element and the anode to the cathode.

and the control element includes an inductance element and the piezoelectric element in series.

10.,The combination of claim 4, characterized in this, that the piezoelectric element is con- 7 nected between a terminal of the anode.

11. The combination of claim 4, characterized in this, that each of the three individual circuits comprises a pair of Lecher conductors.

12. In combination, an electron discharge device having a plurality of electrodes including a cathode, an anode and a control element, and three individual Lecher circuits connected respectively between the cathode and the anode, the cathode and the control element and the anode and control element, the circuit connecting the anode and the control element including a piezoelectric element having a mode of oscillation within the frequency region closely adjacent the resonant frequencies of the other two Lecher circuits, and connections from the Lecher circuits to the electrodes of the discharge device such that the leads to one'common electrode extend in opposite directions and such that the leads to another common electrode extend in the tuned loop and perpendicular directions to minimize external the cathode and control element on the one handand cathode and anode on the other, and means connected to one of the three circuits which overrides the neutralizing characteristic of the circuit to cause oscillation at a selected frequency within that band.

14. A source of high frequency electrical oscillations comprising an electron discharge device having a cathode, an anode and a control element, three individual Lecher circuits connected 

